1. Field of the Invention
The present invention relates to a view point detector, a display unit, a view finder having said display unit and a camera, and more particularly to a sight line detector for detecting the sight line, a liquid crystal display unit for the image display using a liquid crystal material and having means capable of detecting the position on the liquid crystal display unit of the sight line of the observer, a video camera having said display unit, a view finder usable for an electronic camera such as a still video camera, and a camera such as electronic camera.
2. Related Background Art
Conventionally, liquid crystal display units have been employed exclusively for the image display, wherein each display unit is comprised of an image display in a liquid crystal display area 1502 composed of a liquid crystal material and a drive circuit area 1501 having a drive circuit for the image display and provided at least partly around the periphery of the liquid crystal display area, as shown in FIG. 1 which is a typical constitutional view. Liquid crystal display units have been recently utilized for all sorts of electronic apparatuses, including, for example, a display screen for the notebook type computer, a monitor for apparatus, a view finder for videocam coder and so on. In the background, remarkable technical progresses have been made, for example, liquid crystal display units with higher image quality, screens of large size, and mass production technology with reduced costs. However, such progresses only involved the enhancement of display performance, and there was almost no instance of providing additional functions to the liquid crystal display unit.
On the other hand, with the demands from the user side of products, numerous new functions are required for the business equipments and recording apparatuses as mentioned above. In particular, there have been proposed numerous methods of detecting the position at which the user of apparatus (hereinafter referred to as the observer) stares to employ its detection signal for the system control. For example, there is a specific method of using this detection signal as the focusing signal of camera as disclosed in Japanese Patent Publication No. 1-241511.
Referring now to FIG. 2, the outline of a focusing system will be described. FIG. 2 is a typical cross-sectional view showing schematically the constitution of a single lens reflex camera. Light from an object (not shown) is transmitted through an objective lens 701 and reflected at a right angle against a main mirror 702, so that an image is formed on a focusing screen 707 disposed corresponding to a photosensitive member 705 such as a film. The image formed on the focusing screen 707 follows the light path within a pentaprism 708 to pass through an eyepiece 709 to be incident on an observer's eye 715. In FIG. 2, the objective lens at 701 is shown with only a single lens for the sake of convenience, but practically may be comprised of a plurality of lenses as well known. The main mirror at 702 is obliquely disposed in the light path for photographing, or moved out of the light path, depending on the observation (non-photographing) state or the photographing state. A sub-mirror at 703 reflects light flux passing through the main mirror 702 downward toward the bottom of a camera body to be incident on a focus detector 706a. 704a is a shutter, 704b is a diaphragm disposed within the objective lens 701, and 704c is a drive mechanism for moving the objective lens 701 to effect focusing in a light axial direction. 705 is a photosensitive member, for example, a film of silver salt, a solid-state image pickup device using CCD or MOS-type transistor, or an image pickup tube such as a vidicon. 706a is a focus detector capable of detecting the focal point at a plurality of positions on the sight line for photographing. 706b is an exposure value detecting unit comprising an image forming lens and a light receiver allowing for the separate metering. The image forming lens relates conjugately the focusing screen 707 disposed on a predefined image forming plane for the objective lens 1 to the light receiver via the light path within the pentaprism 708. The output of the light receiver is sent to a microprocessor mp which can change the weighting to have a photometry sensitivity distribution around a plurality of central points.
Rearward of an exit plane of the pentaprism 708 for changing the finder light path, an eyepiece 709 is disposed, and used for the observation of the focusing screen with the observer's eye 715. 710 is a beam splitter, using a dichroic mirror for reflecting infrared ray, for example, which is provided within the eyepiece 709. 711 is a condenser lens, 712 is a beam splitter such as a half-mirror, 713 is an illuminating light source such as an LED, which preferably emits the infrared (and near infrared) ray. A light flux emerging from the illuminating infrared light source 713 is passed along the finder light path as parallel light, for example, by virtue of the power of the condenser lens 711 and the back face of the eyepiece 709 (the lateral side of the observer). 714 is a photoelectric converter which is disposed relative to the back face of the eyepiece 709 and the condenser lens 711 to be conjugate to the front eye part of the observer's eye, or particularly the neighborhood of a pupil, when the observer peeps through the eyepiece 709 properly. That is, one method is to dispose the appoint neighborhood of a finder optical system (708, 709) and the photoelectric converter 714 conjugately, preferably with the imaging power of 1 or less.
With the above constitution, an imaging light flux passing through the objective lens 701 is partially transmitted through the main mirror 702 and thus divided into a finder light flux and a focus detecting light flux. The focus detecting light flux is transmitted through the main mirror 702, and then reflected against the sub-mirror 703 to be incident on the focus detector 706a. In photographing, the main mirror 702 is turned upward, and the sub-mirror 703 is folded up over the main mirror. And the film 705 is exposed to light for a predetermined time while a shutter vane 704a is opened and then closed.
On the other hand, the finder light flux passes through the focusing screen 707 and enters the pentaprism 708. Herein, a Fresnel lens integral with or separate from the focusing screen may be disposed near the pentaprism 708. The light flux is incident on the eye of the observer 715 who views an object image projected on the focusing screen 707 by enlarging it by virtue of the dioptric-correction eyepiece 709.
The light path of a sight line detection system is as follows. An illuminating light emitting from the illuminating infrared light source 713 is transmitted through the half-mirror 712, collimated to some degree, and reflected from the mirror 710 to travel along the finder light path. It is desirable from the respects of finder brightness and illumination efficiency of the sight line detection system that the beam splitter 710 can transmit the finder light in visible range coming from the object, and the dichroic mirror can reflect illuminating light in infrared range. However, it is possible to substitute an ND half-mirror by considering on design that if using an infrared light source having too high luminance, the illumination efficiency decreases. Illuminating infrared light introduced into the finder light path passes through the back face of the eyepiece 709 to illuminate the observer's eyeball. Herein, it is expedient to make the illuminating light a substantially parallel light flux in entering the eyeball, so that the illumination condition can be unchanged if the position of observer's eye varies. This can be implemented by adjusting the power arrangement of each portion by utilizing the power of the lens 711 placed ahead and the power of the back face of the eyepiece 709 together.
Reflected light from the observer, which follows the reverse path, is transmitted through the mirror 710 and the lens 711, and reflected from the half-mirror 712 to enter the photoelectric converter 714. Herein, it is desirable that an infrared transmission filter for cutting off the visible light is inserted in the light path from the site where reflected light is separated from the finder light path to the site where it is received by the photoelectric converter. This is intended to cut off visible light of finder image reflected from the cornea to convert photoelectrically only reflected infrared light which is meaningful as the light signal. A photoelectric plane is placed at a site where the neighborhood of a crystal lens or pupil of the observer's eye is imaged with the total power of the lens 711 and the back face of the eyepiece 709. Thereby, light acceptance is performed in the state where Purkinje's first, second, and fourth images are formed, whereby the amount of reflected light is not necessarily weak. The third image does not greatly contribute to the photoelectric conversion signal because it is defocused and light is diffused.
In order to implement the above system when the liquid crystal display unit is used as the image display, it is important to incorporate a sight line detection function, without increasing the number of components as well as the total size of unit, by accumulating photoelectric conversion devices in a portion of the liquid crystal display unit.
However, the conventional active-type liquid crystal display unit used TFTs for the driving of liquid crystal, but conventionally, TFT is composed of polysilicone, amorphous silicone, or single crystal silicone, with its film thickness being about several hundreds .ANG. to 1 .mu.m. On the other hand, to make efficient photoelectric conversion of infrared ray, it is necessary to have the thickness of about several .mu.m for polysilicone and amorphous silicone, and for single crystal silicone, the thickness of 5 .mu.m at minimum. Because the light used for the sight line detection was an extremely weak signal, the integration of a liquid crystal display and a photoelectric converter was virtually impossible.
That is, it was difficult that both an image display area capable of transmitting visible light to operate TFTs (Thin Film Transistor) and a photoelectric conversion area capable of making photoelectric conversion for the sight-line detection by absorbing light enough were provided on the same substrate, and fabricated in a manufacturing process as simple as possible, as long as conventional liquid crystal displays were used.
Next, one example of the sight line detection method will be described below with reference to FIGS. 3 and 4.
FIG. 3 is a principle view of the sight line detection method.
In the figure, 204 is a light source such as a light emitting diode for emitting infrared ray insensitive to the object, which is disposed on the focal plane of a projection lens 206.
Infrared ray emitted from the light source 204 is made a parallel light by the projection lens 206, and reflected against the half-mirror 205 to illuminate a cornea 201 of an eye ball 200. At this time, a Purkinje image d based on a part of infrared ray reflected from the surface of the cornea 201 is transmitted through the half-mirror 205 and converged by a light receiving lens 207 so that the Purkinje image d is formed again at a position d' on an image sensor 209. Also, a light flux from the ends a, b of an iris 203 is introduced via the half-mirror 205 and the light receiving lens 207 onto the image sensor 209, where an image on the ends a, b is formed at the positions a', b'.
When the rotational angle .theta. of the eye ball's optical axis with respect to the optical axis of the light receiving lens 207 is small, the coordinate Zc of the central position c of the iris 203 can be expressed as: EQU Zc.about.(Za+Zb)/2
where Za and Zb are Z coordinates of the ends a, b of the iris 203, respectively. Supposing that the Z coordinate of the position d where Purkinje image occurs is Zd, and the distance from the center of curvature o for the cornea 201 to the center of the iris 203 is Loc, the rotational angle .theta. of the eye ball's optical axis can substantially satisfy the relation: EQU Loc.multidot.sin .theta..about.Zc-Zd (1)
Therefore, the rotational angle .theta. of the eyeball's optical axis can be obtained by detecting the position of each feature point (each of images Za', Zb', Zd' on the image sensor 209 projected from the occurrence position d of Purkinje image and the ends a, b of the iris 203). Then, the above expression (1) can be rewritten as: EQU .beta.Loc.multidot.sin .theta.=(Za'-Zb')/2-Zd' (2)
Where .beta. is a magnifying power as determined by the distance L.sub.1 between the occurrence position d of Purkinje image and the light receiving lens 207 and the distance L.sub.0 between the light receiving lens 207 and the image sensor 209, which is normally a substantially constant value.
In this manner, by detecting the sight line (gazing point) of the observer's eyeball 200, it is possible to know at which point the photographer is staring on the focusing screen in the single lens reflex camera or video camera, for example.
In the above example, the detection of Purkinje image often becomes difficult because another peak output value appears at a position other than Purkinje image due to leak light from the external into the finder or reflection of illuminating infrared ray against the eyelashes.
The above phenomenon will be described below with reference to FIGS. 4A and 4B.
FIG. 4A is an output of the image sensor 209 without leak light such as external light, where d is Purkinje image, a, b is the boundary between the pupil and the iris 203, and i, h is the boundary between the iris 203 and the sclera 202.
If the external light is imaged on the image sensor 209, the output state is as shown in FIG. 4B, with a peak arising at the position f. Accordingly, this peak can not be distinguished from original Purkinje image, so that the sight line detection often fails.